Serum Lipid Modification Related to Exercise and Polyunsaturated Fatty Acid Supplementation in Jumpers and Thoroughbred Horses

The importance of polyunsaturated fatty acids (PUFAs) within the different biological functions of animals has been widely recognized. In this study, exercise and PUFAs supplementation effects on serum triglycerides, total cholesterol, and nonesterified fatty acids (NEFAs) concentration were evaluated in athletic horses. Two sport horse types (10 Italian saddle jumpers and 10 Thoroughbreds) were equally divided into two groups. Jumpers and Thoroughbred experimental groups (A_J and A_T) received 4-week PUFAs supplementation and control groups (B_J and B_T) received no dietary supplement. Before starting the PUFAs supplementation (T0) and at the end of the experimental period (T4), horses were subjected to simulated events. From each subject, blood samples were collected every 7 days at rest, before and after the first test (T0_R and T0_PE), and before and after the second test (T4_R and T4_PE). Higher triglycerides and NEFA concentrations at T0_PE and T4_PE than T0_R and T4_R in both groups were found as a result of exercise (P < .005), but lower triglycerides and NEFA concentrations at T4_PE in group A_J than group B_J (P < .05) and in group A_T (P < .005) than group B_T were found as a result of PUFAs supplementation. Effects of PUFAs supplementation was highlighted by the statistically significant lower triglycerides and NEFA concentrations found at T4_PE than T0_PE in groups A_J (P < .05) and A_T (triglycerides: P < .05; NEFAs: P < .0001).     

Salivary Cortisol Concentration in Exercised Thoroughbred Horses

Both physical activity and stress result in an increase in plasma cortisol level. The measurement of cortisol in plasma requires taking blood samples, which is stressful itself. Therefore, the aim of this study was to evaluate the use of saliva sampling for the determination of cortisol concentrations, indicating the intensity of exercise in horses during race training. Twelve Thoroughbred horses aged 2-3 years were examined during their speed training sessions. The horses galloped on the 1,200-m sand track at a speed of 14.4-15.3 m/s. Three saliva samples and three blood samples were collected from each horse. Both types of samples were taken when the horse was at rest, immediately after returning from the track and 30 minutes after the end of exercise. Blood lactic acid (LA) concentration was determined using the enzymatic cuvette test. The concentrations of cortisol in saliva and plasma samples were measured by enzyme immunoassay methods. Statistically significant correlations were found between salivary cortisol level determined 30 minutes after the end of exercise and blood LA concentration obtained immediately after exercise (P = .003) and between salivary and plasma cortisol levels measured 30 minutes after the end of training session (P = .015). The measurement of cortisol concentration in saliva samples taken from race horses 30 minutes after the end of exercise can be recommended for use in practice under field conditions to estimate the level of relative intensity of exercise in race horses.     

Effect of Acute Administration of Clenbuterol on Athletic Performance in Horses

The aim of the study was to determine the effect of clenbuterol on the anaerobic threshold of horses on a treadmill with increasing physical stress, measuring heart rate (HR) and blood levels of lactate, glucose, and insulin. Twelve Arabian horses were submitted to two physical tests separated by a 10-day interval. Clenbuterol (CL) at 0.8 μg/kg or saline (control—C) was administered intravenously 30 minutes before the test. The treadmill exercise test consisted of an initial warmup followed by a gradually increasing effort. There was no statistical difference in either V₂ or V₄ (velocity at which plasma lactate concentration reached 4 and 2 mmol/L, respectively) between the two experimental groups. For the CL group, V₂₀₀, V₁₈₀, V₁₆₀, and V₁₄₀ (velocity at which the rate heart is 140, 160, 180, and 200 beats/minute, respectively) decreased significantly. At rest as well as times 4, 6, and 10 minutes, insulin levels were higher in the group that received clenbuterol (P < .05). Contrary to what was expected, apparently, there was no improvement in aerobic metabolism in animals when given a therapeutic dose of the bronchodilator. The elevated heart rate observed could have been attributable to the stimulation of cardiac β₁ adrenoceptors and the increased insulin levels to the stimulation of pancreatic β₂ receptors.     

Effect of Recovery Periods during Conditioning of Horses on Fitness Parameters

The effect of recovery from training has not been studied in horses. Therefore, the effect of recovery was examined with exercise of known effect within a conditioning period (CP). A standardized exercise test was performed at the beginning of CP to determine v₄, v₁₀, and v₁₈₀ (horse’s speed, which produced a blood lactate concentration of 4 and 10 mmol/L and a heart rate of 180 beats/min). Six horses were conditioned for three periods of 2 weeks, 5 times per fortnight at their individual v₁₀ for two bouts of 5 minutes on a treadmill. Every 2 weeks of conditioning was followed by 1 week with reduced workload. Standardized exercise test was repeated after each 2 weeks of conditioning and 2 weeks after finishing CP. Exercise speed was individually adapted to the new v₁₀ for every 2 weeks of conditioning. In addition, peak oxygen consumption before, after 3 weeks of conditioning, and at the end of the CP was measured. The mean v₄ increased steadily during CP. v₁₈₀ did not change, whereas peak oxygen consumption increased between the beginning and after 3 weeks of conditioning and leveled off thereafter. In conclusion, reducing the workload for 1 week after 2 weeks of conditioning 5 times per fortnight at v₁₀ for two bouts of 5 minutes allowed for a continuous increase of v₄, but the extent of the increase was smaller than in another study with a similar conditioning program but for the recovery week. The effect of recovery from training needs further studies.     

Relative Flow-Time Relationships in Single Breaths Recorded After Treadmill Exercise in Thoroughbred Horses

Analysis of individual breaths after exercise has potential for pulmonary function testing. The aims of this study were to investigate the dependence of measurements of pulmonary function in single breaths on time postexercise and tidal volume (V_T) after treadmill exercise. Five Thoroughbred horses without evidence of airway disease were used. Horses had been previously acclimated to treadmill exercise and to wearing a face mask. A Quadflow spirometer recorded airflow rates continuously during 90 seconds after intense treadmill exercise to fatigue. Indices of function were based on ratios of times within each breath and analyses of the shape of relative flow–time curves within inspiration and expiration. Restricted maximum likelihood, general linear regression, repeated-measures one-way analysis of variance (ANOVA), and two sample t-tests were used, with statistical significance at P < .05. Time postexercise had no effect on several ratios based on time for inspiration (T_I) and expiration (T_E), and times to peak flows (T_I/T_T, T_E/T_T, T_E/T_I, Tpef [peak expiratory flow]/T_E, and Tpif [peak inspiratory flow]/T_I). Many variables were significantly dependent on V_T. Occasional big respiratory cycles with V_T more than 10% greater than in the previous breath had significantly different means for relative flow (Rf)/(T_E/T_I), epz_50% (50% of the time from Tpef to end of expiration), epz_75% (75% of the time from Tpef to end of expiration), and ipz_75% (75% of the time from Tpif to end of inspiration). Predicted means for these variables differed by 10–20%. This study establishes guidelines for the selection of breaths after exercise, and describes a new approach to measurement of relative flow and time relationships. It was concluded that several time-based ratios have potential for measuring pulmonary function. However, care is needed when selecting breaths for calculation of most of the new relative flow–time variables.     

Comparison of Insulin Sensitivity of Horses Adapted to Different Exercise Intensities

Diets high in concentrates and soluble carbohydrates are associated with reduced insulin sensitivity in horses. Exercise training could protect against diet-induced insulin resistance. The objective of this study was to determine the intensity of exercise training required to affect insulin sensitivity in stabled horses fed a diet high in concentrates but moderate in soluble carbohydrates. In all, 31 stabled horses underwent three different exercise regimens: turnout, light exercise, and moderate exercise, while being fed a diet containing 60% concentrate. Blood was sampled monthly and analyzed for insulin. Insulin sensitivity was assessed using basal insulin concentrations and calculated insulin sensitivity (reciprocal of the square root of insulin) and compared across months by analysis of variance with repeated measures. Insulin sensitivity (reciprocal of the square root of insulin) was higher during periods of moderate and light physical activity as compared with turnout. These results indicate that turnout alone may not be adequate to improve insulin sensitivity in horses fed high amounts of concentrate.     

Nutrition and Exercise in the Management of Horses and Ponies at High Risk for Laminitis

Obesity, insulin resistance (IR) and hyperinsulinemia are risk factors for laminitis in horses and ponies. Alterations in management, especially diet and physical activity, can be helpful in the management of these risk factors. Caloric restriction, ideally combined with increased physical activity, to promote weight loss and improve insulin sensitivity is indicated for the management of obese animals. Strict control of dietary NSC through the elimination of grains and sweet feeds and by restricted access to NSC-rich pastures is recommended for insulin-resistant animals, regardless of whether they are obese or not. Medical treatment with levothyroxine or metformin may be indicated in obese or insulin-resistant animals that do not respond to conservative management.     

A case-crossover study of intensive racing and training schedules and risk of catastrophic musculoskeletal injury and lay-up in California Thoroughbred racehorses

The objective of this study was to investigate the relationship between intensive racing and training schedules and risk of either catastrophic musculoskeletal injury (CMI) or lay-up from racing in California Thoroughbreds. Thoroughbred racehorses that sustained a CMI during racing or training and either were subsequently euthanized or died on a California racetrack during 1991 and 1992 were studied using a case-crossover study design. Each study subject (case) provided its own self-matched control information in the form of ‘typical’ exposure frequency, determined or estimated from historic information. Periods of rapid average daily accumulation of high-speed exercise distance were identified for each horse from official race and training histories with a sliding 60-day window. Those window frames containing an average daily rate of distance accumulation exceeding 75th percentile cutoff values were classified as exposed frames followed by 30 days of increased risk, or hazard periods. All remaining days (excluding periods of layoff from racing) were considered non-hazard time at risk. The relative risk (RR) of CMI within 30 days following a period of rapid accumulation of high-speed exercise distance (during a hazard period) was 4.2 (95% confidence interval [CI]= 3.0, 5.8). Of these 214 cases, 84 (39%) were injured during a hazard period whereas on average only 22% of total career time at risk was hazard time for these horses. A second analysis was performed for horses with at least 1 lay-up period from racing of ≥ 60 days. RR for a lay-up beginning during a hazard period was estimated for the last lay-up experienced by each horse. The RR for lay-up beginning during a hazard period was 4.8 (95% CI = 2.9, 8.1). Of these 98 cases, 32 (33%) of the lay-ups began during a hazard period whereas on average, only 22% of at-risk time up to last lay-up was hazard time for these horses.     

Aminophylline Affects Glycemia Control and Increases Anaerobic Glycolysis in Horses during Incremental Exercise

A study was conducted on the effects of acute administration of aminophylline on physiological variables in purebred Arabian horses submitted to incremental exercise test. Twelve horses were submitted to two physical tests separated by a 10-day interval in a crossover study. These horses were divided into two groups: control (C, n = 12) and aminophylline (AM, n = 12). The drug at 10 mg/kg body weight or saline was given intravenously, 30 minutes before the incremental exercise test. The treadmill exercise test consisted of an initial warmup followed by gradually increasing physical exigency. Blood samples were assayed for lactic acid, glucose, and insulin. Maximal lactic acidemia was greater (P = .0238) in the AM group. Both V₂ and V₄ (velocities at which lactate concentrations were 2 and 4 mmol/L, respectively) were reduced in the AM group by 15.85% (P = .0402) and 17.76% (P = .0109), respectively. At rest as well as at 4 minutes, insulinemia was greater in the AM group (P = .0417 and .0393). Glycemia was statistically lower in the AM group at times 8 (P = .0138) and 10 minutes (P = .0432). Use of aminophylline in horses during incremental exercise does not seem to be beneficial, because this drug has a tendency to cause hypoglycemia and to increase dependence on anaerobic glucose metabolism.     

Heart Rate Variability in Horses Engaged in Equine-Assisted Activities

Although there has been a recent surge in using horses to treat mental and emotional human health issues, the consequences of horse-assisted interventions on the stress response of horses have not been well documented. Assessment of the autonomic nervous system and its regulation of cardiovascular function has been used as an indicator of acute and chronic stress in human beings and horses. Heart rate variability (HRV) is a noninvasive measurement that has been used to assess autonomic nervous system regulation of cardiovascular function. There is evidence to suggest that several factors including the genotype, behavior, environment, temperament, and nutritional status of the horse play a key role in the large inter-individual variations in basal HRV. The present study determined whether 24-hour HRV recordings in horses currently working in equine-assisted therapy (EAT) differ from those previously shown in Thoroughbred horses. Findings from the present study found that in contrast to previous studies in Thoroughbred horses, diurnal and nocturnal low frequency and high frequency powers were not significantly different in horses that are currently engaged in EAT. Future studies are needed to determine the short- and long-term consequences of horses participating in EAT programs. Findings from this study will provide the basis for the development of a physiological/behavioral assessment criteria to determine the consequences of EAT on the well-being of horses as well as to help EAT Centers to improve the beneficial effects of EAT in human beings.     

Heart Rate,Net Cost of Transport,and Metabolic Power in Horse Subjected to Different Physical Exercises

Considering that workload can also be expressed in terms of estimated net transport cost (COT), the metabolic energy needed to transport unit mass of animal unit distance, the aim of our study was to describe the heart rate (HR), COT, and the total metabolic power requirement per kilogram (P) during different exercises (aerobic, anaerobic, and aerobic–anaerobic exercises). On the basis of their attitude, 25 horses, divided into five equal groups, traveled a distance of 6,000 m, walking at 100 m/min in a horse walker (group A); performed 20-minute treadmill walk at 130 m/min, average speed up gradient of 5% (group B); performed a 700-m-long show jumping course with 13 fences (group C); traveled a distance of 2,100 m galloping at a speed of 700 m/min (group D); and traveled a distance of 2,000 m trotting at a speed of 660 m/min (group E). On each horse, HR was continuously recorded by means of an equine HR monitor. COT was calculated with the following formula: (HR − 35) kg⁻¹ m⁻¹ 10³; P was calculated applying the formula: (HR − 35) min⁻¹ kg⁻¹. COT and P values, estimated from the mean HR, measured continuously during each experimental condition showed no linear relationship with HR and speed. The use of combined weight of horse and tack (group C and D) and horse, tack, and sulky (group E) statistically changed the results of formula application. COT and P change in different exercises and provide additional information about performance in athletic horses.     

Effect of Ergovaline Ingestion on Recovery of Horses Subjected to an Anaerobic Standard Exercise Test

The objective of this study was to determine whether consumption of tall fescue seed which contained high levels of ergovaline would affect post-exercise recovery of horses subjected to an anaerobic exercise test. Ten Quarter horses were separated into two groups and fed alfalfa hay, commercial sweet feed, and either endophyte-infected (E+) or endophyte-free (E−) ground tall fescue seed. Diets contained 11.8% seed, which resulted in 459 ppb of ergovaline for the E+ diet. During the first 28 days, horses in group A received E+ and group B received E−. Diets were reversed during the next 28 days (crossover design). Horses were ridden for 5 days per week. On day 14, 28 (period 1), 42, and 56 (period 2), they were subjected to a standardized exercise test (SET) that consisted of 41 turns in 4 minutes and was designed to raise the horse’s heart rate (HR) beyond the anaerobic threshold (150 bpm). There was a horse effect (P < .05) on post-SET respiration rate, HR, and post-exercise whole blood lactate level, but not rectal temperature (RT). For these variables or period effects, there was no horse × treatment, period × treatment, or period × horse interactions (P < .05). Treatment had no effect on whole blood lactate level, RT, or HR at any time measured. Respiration rate did not vary by treatment at rest or 1 minute after SET but was higher for the E+ treatment at 5 and 10 minutes after SET (P < .005). Consumption of diets that averaged 450 ppb of ergovaline caused the horses expend more respiratory effort in an attempt to recover to resting RT.     

Fecal pH and Microbial Populations in Thoroughbred Horses During Transition from Pasture to Concentrate Feeding

Abrupt dietary transitions and feeding of rapidly fermentable diets are common practices in the horse industry and have been associated with digestive and metabolic disorders that can impair the performance of horses. The present study investigated the effect of dietary transition from pasture grazing to confinement with concentrate feeding, and back, on fecal pH and bacterial populations of Streptococcus spp and Lactobacillus spp. Six Thoroughbred fillies, previously grazing perennial ryegrass and white clover-based pasture, were housed in individual stalls and fed an increasing ratio of concentrate to conserved forages for 13 days (days 1-13), followed by an abrupt transition back to only pasture-grazing for 3 days (days 14-16). The concentrate was initially offered at 0.83 kg dry matter (DM)/d and increased to 5 kg DM/d, whereas ensiled alfalfa was initially offered at 0.61 kg DM/d, increasing to 1.22 kg DM/d. Meadow hay was initially offered at 6.73 kg DM/d, decreasing to 1.6 kg DM/d. Fecal specimens were collected daily for determination of pH, and every 2 days for quantitative analysis of Streptococcus spp and Lactobacillus spp. Mean fecal pH increased significantly from pasture baseline values (pH 6.18) during the initial confinement and supplementation on day 1 (6.37), day 2 (6.52), day 3 (6.58), and day 4 (6.43) (standard error of mean [SEM]: 0.056; P < .001). By day 5, mean fecal pH values had decreased to, and remained at, baseline values until the horses returned to pasture, when another increase occurred at day 15 (6.45). Fecal colony forming units (cfu) of Streptococcus spp and Lactobacillus spp increased linearly (r = 0.94; P < .001) from 6.0 and 6.1 log₁₀ cfu/g on day -4, to 7.8 log₁₀ cfu/g on day 14 (SEM: 0.2 P < .001), respectively. Fecal cfu decreased on return to a pasture-only diet (P < .001). In this study, the increment of bacterial populations was associated with a relatively stable fecal pH and highlights the difficulty in identifying the effects of dietary transition on the equine hindgut health, without microbial culture.     

Cardiac Power Output during Dobutamine Stress Test in Horses

Although echocardiography has greatly improved the diagnostic possibilities in equine medicine, determining the prognosis remains a difficult task. In humans, maximal cardiac power output (CPO) has been described as a powerful indicator of exercise capability and outcome in heart disease. The aim of the study is to describe the measurement of CPO by echocardiography and by thermodilution in healthy horses. Six healthy horses were studied. Cardiac output (CO) was measured by thermodilution and Doppler echocardiography at rest and during a pharmacologic stress test consisting of 35 μg/kg atropine followed by incremental steps 2, 4, 6, and 8 μg/kg/min of dobutamine infusion. Mean arterial pressure (MAP) was measured invasively by a catheter introduced into the transverse facial artery. CPO was calculated as the product of CO and MAP. Baseline CPO measured by thermodilution and by Doppler echocardiography was 10.7 ± 3.3 and 13.7 ± 4.5 watts, respectively. CPO increased significantly with pharmacologic stimulation and reached maximal CPO of 66.4 ± 3.6 and 60.4 ± 5.1 watts when measured by thermodilution and Doppler echocardiography, respectively. This study describes an estimation of CPO in horses. Further studies should demonstrate the usefulness of CPO as a predictive indicator in horses suffering from cardiac disease.     

Inhibition of Nitric Oxide Synthase with L-NAME Does Not Increase Lactate Production at Rest or During Short-term High-intensity Exercise in Thoroughbred Horses

The present study was carried out to determine whether inhibition of nitric oxide (NO) synthase promotes anaerobic metabolism in exercising horses, resulting in a significantly increased blood lactate concentration. N -nitro-L-arginine methyl ester (L-NAME) is a potent inhibitor of NO synthase that has been tested in horses and other species. Two sets of experiments, namely placebo (saline control) and L-NAME (20 mg/kg, IV) studies, were carried out on seven healthy, sound, exercise-trained, Thoroughbred horses in random order, 6 to 7 days apart. In both experiments, an incremental exercise protocol was used and data were obtained at rest, during submaximal exercise performed at 8 m/s on a 4.5% uphill grade, and during galloping at 14 m/s on a 4.5% uphill grade – a workload that not only elicited maximal heart rate and induced exercise-induced pulmonary haemorrhage, but also could not be sustained for more than 90 s. Measurements were also made in the recovery period. Mixed-venous blood samples, obtained at matched intervals in the two sets of experiments, were analysed in triplicate for determining the lactate concentration. Following administration of L-NAME, significant bradycardia occurred at rest (27±1 vs 37±2 beats/min in the placebo trials; p<0.0001) as well as during submaximal exercise (183±4 vs 200±4 beats/min in the placebo trials; p<0.001), but the heart rate increased during galloping at 14 m/s on a 4.5% uphill grade to reach values observed in the placebo trials (215±2 beats/min) and significant differences were not found. At rest, the mixed-venous blood lactate concentration was similar in the two experiments. With exercise, the mixed-venous blood lactate concentration increased progressively as work intensity increased in both trials, but significant differences were not found between the placebo and the L-NAME experiments during submaximal exercise, near-maximal exercise or recovery. These experiments demonstrated that inhibition of NO synthase in Thoroughbred horses does not promote enhanced anaerobic metabolism at rest or during short-term incremental exercise leading to galloping at maximal heart rate.     

Effect of Ergopeptines Associated with Tall Fescue Ingestion on Recovery of Horses Subjected to Standardized Exercise Tests

Ten horses were paired by body weight, age, and skill level, and one of each pair was assigned to one of two groups. Horses were fed alfalfa hay and a mixture of commercial sweet feed and pellets. Horses in group A were fed fescue seed that contained both ergovaline and ergotamine (E+), whereas those in the other group were fed seed that was free from ergot alkaloids (E−). After the first 35 days, horses were switched to the opposite seed treatment. Seed was fed at 8.2% of the diet, resulting in 406 ppb of ergotamine plus ergovaline in the E+ diet. During weeks 3, 5, 7, and 10, horses were subjected to two separate standardized exercise tests (SETs). The aerobic test consisted of walking, trotting, and loping and was designed to maintain horse's heart rate (HR) to less than 150 beats per minute (bpm). The anaerobic test consisted of 40 turns in less than 4 minutes in response to the movements of a mechanical cow and was designed to increase the horse's HR to more than 150 bpm. There were no treatment effects on water consumption or sweat production. There were also no treatment effects on rectal temperature at rest or during recovery from the anaerobic SET. However, rectal temperatures were higher (P < .05) 1 and 30 minutes after the aerobic SET for horses consuming E+ seed. When horses were on the E+ treatment, HRs were lower (P < .05), both at rest and during the SET. HRs were also lower (P < .05) for the E+ treatment at 1 minute after the aerobic test and 5 and 10 minutes after the anaerobic test. Respiration rates were higher (P < .05) 30 minutes after the aerobic SET and 30 and 60 minutes after the anaerobic SET for the E+ treatment. Horses may have increased respiration rates to compensate for a reduction in the efficiency of evaporative cooling, which resulted from vasoconstriction of peripheral blood vessels.